1. Field of the Invention
The present invention relates to a light-sensitive and heat-sensitive recording material, and particularly to a diazo compound based light-sensitive and heat-sensitive recording material on which an image can be fixed.
2. Description of the Related Art
A diazonium salt compound is a compound having extremely high chemical activity, and reacts with a compound (which is called a coupler) having a phenol derivative or an active methylene group, to easily form an azo dye. Further, a diazonium salt compound also has photosensitivity, and is decomposed by irradiation with light and loses its activity. Therefore, diazonium salt compounds have been conventionally used for a long time as light recording materials as represented by diazo copy (see "Shashin-Kougaku no Kiso--Hi-gin-en Shashin Hen (Fundamentals of Photographic Engineering--Non-silver Salt Photography Section)", pp. 89 to 117, 182 to 201, edited by the Photographic Society of Japan, Corona Publishing Co., Ltd. 1982).
Further, in recent years, diazonium salt compounds are also applied to recording materials on which fixation of an image is required, by utilizing its nature in which it is decomposed and loses activity due to action of light. As a typical example, there has been proposed a light fixation type light-sensitive and heat-sensitive recording material in which a diazonium salt compound and a coupler are heated in accordance with an image signal so as to be reacted to form an image, and thereafter, the image is fixed by irradiation with light (Hirotsugu Sato et al., Bulletin of the Image Electronics Society, Vol. 11, No. 4 (1982) pp. 290 to 296, and the like).
However, this recording material in which a diazonium salt compound is used as a color forming element has a drawback in that a shelf life thereof as a recording material is short since the activity of the diazonium salt compound is extremely high and the diazonium salt compound is thermally decomposed gradually to lose its reactivity even in a dark place. As one of the means for solving the drawback, there is suggested a method in which a diazonium salt compound is enclosed in a micro capsule. In this method, the diazonium salt compound can be isolated from materials which promote decomposition, such as water, a base, and the like. Therefore, the shelf life of the diazonium salt compound as a recording material can be greatly increased (Tomomasa Usami et al., Bulletin of the Electronic photography Society, Vol. 26, No. 2 (1987), pp. 115 to 125).
In a case in which a micro capsule has a wall composed of a material having a glass transition temperature such as a urea resin or urethane resin, which glass transition temperature is slightly higher than room temperature, this micro capsule is called a heat-responsive micro capsule and is useful for a light-sensitive and heat-sensitive recording material since the capsule wall is impermeable with respect to materials at room temperature and is permeable with respect to materials at a temperature equivalent to or greater than the glass transition temperature thereof. Namely, by preparing the recording material in which a heat-sensitive recording layer including a coupler, a base, and the heat-responsive micro capsule which contains a diazonium salt compound is applied to a substrate, the diazonium salt compound can be stably kept for a long period of time, and a color formation image can be easily formed by heating. Further, an image can be fixed by irradiation with light.
As described above, stability of a diazonium salt compound can be remarkably improved by enclosing the compound in a micro capsule.
However, even in the light-sensitive and heat-sensitive recording material in which the compound is enclosed in a micro capsule, various photo-dissociative reaction products are formed during diazo decomposition in a fixing process, and coloring (so-called photo-dissociative stain) having an absorptivity, particularly in a visible region, may occur. Further, when such recording materials are exposed to the sun or a fluorescent light for a long time after fixing of an image, the density of the non-image portion (a base portion) also becomes higher and the whiteness of the recording paper may remarkably decrease.
Further, heat development-type recording materials using diazonium salt compounds also have a drawback in that after optical writing and heat development, photo-dissociative stain occurs in a non-image portion to thereby cause deterioration in the whiteness of the base portion, in the same manner as in the above-described light-sensitive and heat-sensitive recording material.
In order to improve the whiteness of the base portion, for example, Japanese Patent Application Laid-Open (JP-A) No. 62-55188, discloses that a micro capsule containing a diazo compound and a compound which forms free radicals by irradiation with light (that is, aromatic ketones such as benzophenone, 4,4'-bis(dimethylamino)benzophenone, and the like, cyclic aromatic ketones such as fluorenone, anthrone, and the like, quinones such as benzoquinone, 2,3,5-trimethyl-6-bromobenzoquinone, and the like, benzoin, benzoin ethers, aromatic polycyclic hydrocarbons, azos such as azobisisobutyronitrile, organic sulfides such as thiuramdisulfide, and acyloxime esters). By using the above-described compound, which forms free radicals, the whiteness of the base portion after fixing was improved to a certain degree.
However, as advanced light-sensitive and heat-sensitive recording materials have been desired, further improvement has been demanded for the whiteness of the base portion in a fixed light-sensitive and heat-sensitive recording material.
An object of the present invention is to provide a light-sensitive and heat-sensitive recording material containing a diazo compound and a coupling component, in which a density of an image recorded thereon and the whiteness of a base portion are both improved.